Recently, LEDs have been used as a light source for vehicles in view of their increased light luminosity, reliability, and longevity. A plurality of LEDs are often used in a flat plane arrangement. For example, FIG. 10(a) shows LEDs used in a tail lamp for a two-wheeled vehicle. A plurality of LEDs 20 are mounted on a circuit board 15X and arranged longitudinally and laterally in a flat plane. The circuit board 15X is mounted inside a lamp body (not shown), and light from the LEDs radiates through lenses attached on the opening of the front side of the lamp body.
The number of LEDs used in the lamp is increased as the emission area required for the lamp increases. In FIG. 10(a), a plurality of LEDs 20 are arranged on the circuit board 15X in a flat plane and are connected in series to form LED lines L21 to L26, based on the relationship between power supply voltage and current that is applied to emit light. A plurality of the LED lines L21 to L26 are connected in parallel to form an LED group. By connecting each of the LED lines to a switch 31 and an electric power supply 30 via a drive resistance 21, required current is applied to each LED line so that each LED in each LED line can emit light.
However, as shown in FIG. 10(b), once one LED becomes incapable of emitting light (shaded LEDs in the drawing), current is not applied to other LEDs connected by the LED line. Therefore, the overall light intensity is decreased.
In a lamp for two-wheeled vehicles, the lamps may have a right area and a left area, and the areas are configured laterally and symmetrically. When there is a problem with an LED line and renders LEDs incapable of emitting light either in the right or left side area, the difference in intensity of light in the left and right sides.